1. Field of the Invention
This invention relates to wrenches and, in particular, to open wrenches for turning hexagonal or other polygonal fasteners.
2. Description of the Prior Art
Wrenches with open-ended or open-sided hexagonal fastener-engaging cavities (referred to herein collectively as “open” wrenches), are designed to engage hexagonal fasteners by being moved in the direction of the axis of the fastener, or at right angles to the axis. They are not only more convenient to engage, they are able to engage fasteners that other styles of wrenches, such as socket or box wrenches, are unable to engage because the ends of the fasteners are not accessible. Engaging the fastener on a tubing fitting is a good example.
Unfortunately, open-end wrenches are not nearly as strong as box or socket wrenches, but it is desirable to tighten or loosen the fasteners to the same level as socket and box wrenches, if the fasteners are to do their job. Open wrenches, whether with fixed jaws as in the design customarily referred to as “open-end” or with adjustable jaws such as Crescent®, Stillson or pipe wrenches, must meet various design criteria. They must be strong and stiff enough to transmit torque to nuts, bolts and other fasteners with polygonal heads. Both stiffness and strength are important because wrenches can fail either by the jaw breaking, or by the jaw spreading apart in such a manner that the fastener turns, or the fastener turns part way and then the corners of the fastener yield, allowing the wrench to turn the rest of the way without turning the fastener.
Open wrenches have a tendency to spread under load. This lets the fastener rotate in the wrench, which tends to allow the wrench to move relative to the fastener, damaging the corners of the fastener. Under heavy loads, the wrench may move relative to the fastener in such a way that the fastener rotates toward the outside of the wrench opening, which is a much weaker position of engagement, and can result in damage to the wrench or the fastener. Thus, another important feature of open-end wrench design is to keep the fastener fully seated in the wrench opening, preferably touching the base of the wrench opening or throat, so as to minimize the bending moments on the jaws. It is for this reason that it is undesirable to have the fastener “walk” out of the wrench opening as a result of relative rotation of the wrench and fastener. This can occur even if the user has properly positioned the wrench all the way on to the fastener. Shifting may occur under load as a result of the deflections and deformations occurring under load.
FIGS. 1 and 4 illustrate a standard wrench 10 with substantially planar sides or jaws 13, 14 joined to a generally “U” shaped back or throat 18. The wrench is shown in the conventional tightening position, turning or torquing the fastener clockwise. FIGS. 2, 3, 5, 6 and 8 and the solid line view of the fastener in FIG. 7 show wrenches and fasteners in similar positions. The phantom or dotted line view of the fastener in FIG. 7 illustrates the “neutral” or unloaded position. In this position the sides of the fastener are generally parallel to the jaws of the wrench, which do not apply torque to the fastener in either direction.
The fasteners with which the inventive wrench is used are polygonal fasteners having opposing pairs of parallel sides each of which join adjacent sides at a corner. The wrench jaws engage or grip an opposing pair of parallel sides 231, 261. As discussed herein, the corners of the gripped sides proximal the wrench opening are referred to as front side corners 24, 26, and the corners proximal the throat of the wrench are referred to as rear side corners 23, 27. The gripped sides 239, 261 of the fastener have forward portions proximal the wrench opening and rear portions proximal the throat. The fasteners included in the discussion herein are hexagonal in shape, but the invention is not so limited. The corner of a hexagonal fastener proximal the wrench throat is referred to as rear corner 22.
The contact points and forces between the jaws and fastener are interchanged to transmit torque in the opposite direction. Because of this, wrench 10 is symmetrical about the centerline or axis of symmetry CL of fastener-engaging opening 16, as are almost all open-end wrenches.
This wrench is susceptible to the problems discussed above. The curved back avoids stress concentration points, but it reduces the amount of metal in the head 11 of the wrench. This weakens the wrench and reduces its stiffness. As the load is increased, the jaws of the wrench will tend to spread apart elastically and the corners of the fastener will tend to deform both elastically and plastically. To be in static equilibrium, the wrench must make contact with at least two points on the fastener as this is occurring. Since the shapes are changing, there must be relative motion between the wrench and the fastener. This will require rotation about either the left front side corner or point 24 of the fastener or the right rear side corner or point 27, as shown in FIG. 4, on a basis of chance. If rotation happens to occur about point 24, the rear side corner or point 23 of the fastener moves away from contact with the wrench, point 27 moves toward the open end 16 of the wrench, force B moves further out in the opening, and the location of force A remains the same. In that case, the magnitude of forces A and B must increase to apply the same amount of torque to the fastener, because the applied torque is equal to the value of force A times distance a plus the magnitude of force B times the distance b. This increase in force causes the jaws to spread further than they would had the rotation occurred about corner 27. If the rotation occurs at corner 27, contact will still be maintained at point 27, and there will be no significant change in the location and magnitudes of forces A and B. In the wrench shown in FIG. 4, either mode of loading occurs by chance. This invention biases the contacts in such a way that rotation is about point 27 rather than about point 24 when the rotation is clockwise and, therefore, the forces are as shown.
FIG. 2 shows another conventional open wrench 30, which differs from the wrench in FIG. 1 by having a V-shaped back or throat 38, with sharp corners 381, 383 where the throat meets the planar sides 331, 341 of the wrench, and another sharp corner 382 at the central axis X of the fastener-engaging cavity 36. The cross-hatched area between the V-shaped back 38 and the phantom outline of the U-shaped back of the wrench in FIG. 1 is additional metal that strengthens the jaws 33, 34 of wrench 30. Unfortunately, corners 381, 382 and 383 are stress concentration points that weaken this wrench.
A variety of open designs have been adopted or proposed in attempts to provide wrenches that come closer to meeting these goals than conventional polygonal wrenches, which have substantially planar sides and sharp corners. Representative examples are provided by U.S. Pat. No. 3,242,775 to Hinkle, U.S. Pat. No. 5,117,714 to Pagac et al, and U.S. Pat. No. 5,381,710 to Baker. All offer advantages, but all of these designs also suffer from disadvantages. Hinkle provides inclined surfaces at both the inner and outer end of his fastener-engaging surfaces. This reduces the tendency to exert pressure on the corners of the fastener, but it reduces the length of the moment arm of the force couple on the fastener, i.e. the product of the forces applied to the fastener times the lengths of the distances from the force vector to the central axis of the fastener. For example, in the conventional U-shaped wrench shown in FIG. 4, the torque applied to fastener 20 is equal to force vector A times moment arm a plus force vector B times moment arm b. This reduction in Hinkle of the length of the moment arm about the axis of the fastener increases the force that must be exerted by the jaws to generate an equivalent amount of torque. The problem gets worse if the fastener “walks” or slips part way out of the wrench. This lengthens the moment arms m and n on jaws 13 and 14, i.e. the distance from the base of throat 18 to the points where force vectors A and B are applied to the fastener. Like many currently available open-end wrenches, Hinkle does not have any way to grip the side of the fastener securely, which makes his design prone to slip, and increase the force couples on the jaws of the wrench. This increases the risk that the jaws will fail, or be deformed enough to allow the fastener to slip and be damaged.
Pagac et al provide serrations on the fastener-engaging jaws of their wrench. But the jaws also have relief regions to prevent the front corners of the fasteners from contacting the jaws. As with the Hinkle design, this shortens the force couple arm and increases the force and torque that must be applied by the wrench to torque the fastener by the same amount. Baker's curved fastener-engaging jaws suffer from similar problems. If the fastener is not fully seated in Pagac's jaws, the same force must be applied at points further out on the jaws, increasing the bending torque on the jaws of the wrench.
U.S. Pat. No. 5,148,726 (Huebschen et al.), like Pagac et al., comprises an open-end wrench with a curved throat, opposing jaws each having serrated regions near the throat, and a recess or relief region near the opening of the wrench for receiving the corner of a fastener seated in the wrench to protect the corner of the wrench. However, this severely limits the effectiveness of the wrench. When a hexagonal fastener is received in the wrench with one corner near the center of the throat and the wrench is turned to turn the fastener, there is no surface on the wrench to urge the latter corner of the fastener towards the throat. Therefore, the corner of the fastener near the center of the throat of the wrench cannot be driven by the surface of the throat. Therefore, the only corners (or surfaces close to the corners) being engaged by the wrench are the one corner at the foregoing relief region and the corner on the other side of the wrench next to the throat. Moreover, the tip of the serration in U.S. Pat. Nos. 5,117,714 and 5,148,726 closest to the relief region of the wrench embeds itself into the fastener near the corner, and pushes the corner back towards the throat. Moreover, the serrations of the prior art wrenches disclosed in the latter patents engage the fastener first near the corner and proceed to engage the fastener as the wrench turns at increasing distances from the corner. Therefore, wrenches of the foregoing prior art not only detract from the turning force by reason of the relief region, but further damage the fastener as well. The present invention, as discussed below, makes an important improvement in that the wrench engages three—and often four—corners of the fastener and tremendously increases the torque applied to the fastener, the serrations engage the fastener away from the corner and do not damage the fastener as turning force is applied to the wrench.